Larrythe ferro frit is made under exacting standards by Ferro industries so I'll guess not much.Not sure about source of nickle ox but I have not noticed much over the yearsManaganese-I have a new 50# bag but still have not finished (almost my last 50# bag so I cannot say yetRed iron you will not notice it at least in most glazes

The thing to keep in mind is these are all mined from the earth and deposits vary so suppliers may have old or new stock with minute differences-most colorants I feel do not change that much. With a few exceptions like rutileThe frits are reground fired glasses so they are controlled to a huge degree.My old frits are very much like the new ones.If you worry about this just buy lots so you draw for many years from the same bags-also quantity discounts will apply at places like US pigments.comor Laguna Clay Co (colbalts are always high priced there)-I tend to buy colorants at several supply sources as prices vary- my last buy of colbalt Carbonate I bought 100#s and resold 80% of it to our local supplier-it was chinese and I had a great wholesale connection.Mark

I will buy in larger quantities as soon as I'm clear on what glazes I'm going to be using most often. At this point I'm such a beginner that I'm just sorting through dozens of cone six glazes on test tiles to see what looks good in my situation and would be worth keeping.

Most likely you will need copper carbonate as well cobalt carb and iron and rutile and managnese
The others less but still a maybe will be copper oxide as well as cobalt ox and black copper ox
This will be a good start.
Mark

recently in Texas there was a shift in talc. Things do change as the mines go through their veins.
Since you are in the NW , you should be able to get Custer feldspar easily. the Bray carries a lot of chemicals that many suppliers don't carry.
molochite for example.
I always check shipping and price per pound. Irons can vary, copper carbonate can vary.Large quantities are a good idea.

recently in Texas there was a shift in talc. Things do change as the mines go through their veins.Since you are in the NW , you should be able to get Custer feldspar easily. the Bray carries a lot of chemicals that many suppliers don't carry.molochite for example.I always check shipping and price per pound. Irons can vary, copper carbonate can vary.Large quantities are a good idea.

Marcia

MarciaThe shift in talc is/was beyond Texas-its just about everywhere-My matt glaze depends on old school talcs and I have about 5 years supply left. The closest newer talc is serria light from Wyoming and its a little shiny.I only use pioneer talc in one glaze now-seems talc has gone thru so many changes.Gone are c-30 talc and desert talc from the old days.If anyone has some of these I'm a buyer,Mark

I thought that the asbestos talcs where the ones from New York?
seems odd that many where from all over the country
One would think with the chemical analyses they would catch this on the early side
Mark